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authorDaniel Bristot de Oliveira <bristot@redhat.com>2014-07-22 23:27:41 -0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-09-05 16:34:13 -0700
commit8185982aa13b9000ac7c42f936c23cbbb882a31e (patch)
treec26054d7a37b3924d07ecf64c9321174d9fbc8eb /kernel
parentdcb785742a05ffa8be4d00a886daa7ba5d831302 (diff)
downloadlwn-8185982aa13b9000ac7c42f936c23cbbb882a31e.tar.gz
lwn-8185982aa13b9000ac7c42f936c23cbbb882a31e.zip
sched: Fix sched_setparam() policy == -1 logic
commit d8d28c8f00e84a72e8bee39a85835635417bee49 upstream. The scheduler uses policy == -1 to preserve the current policy state to implement sched_setparam(). But, as (int) -1 is equals to 0xffffffff, it's matching the if (policy & SCHED_RESET_ON_FORK) on _sched_setscheduler(). This match changes the policy value to an invalid value, breaking the sched_setparam() syscall. This patch checks policy == -1 before check the SCHED_RESET_ON_FORK flag. The following program shows the bug: int main(void) { struct sched_param param = { .sched_priority = 5, }; sched_setscheduler(0, SCHED_FIFO, &param); param.sched_priority = 1; sched_setparam(0, &param); param.sched_priority = 0; sched_getparam(0, &param); if (param.sched_priority != 1) printf("failed priority setting (found %d instead of 1)\n", param.sched_priority); else printf("priority setting fine\n"); } Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: linux-kernel@vger.kernel.org Fixes: 7479f3c9cf67 "sched: Move SCHED_RESET_ON_FORK into attr::sched_flags" Link: http://lkml.kernel.org/r/9ebe0566a08dbbb3999759d3f20d6004bb2dbcfa.1406079891.git.bristot@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 515e212421c0..677ebad70ce1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3511,9 +3511,10 @@ static int _sched_setscheduler(struct task_struct *p, int policy,
};
/*
- * Fixup the legacy SCHED_RESET_ON_FORK hack
+ * Fixup the legacy SCHED_RESET_ON_FORK hack, except if
+ * the policy=-1 was passed by sched_setparam().
*/
- if (policy & SCHED_RESET_ON_FORK) {
+ if ((policy != -1) && (policy & SCHED_RESET_ON_FORK)) {
attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
policy &= ~SCHED_RESET_ON_FORK;
attr.sched_policy = policy;